[gdb/testsuite] Fix minimal encodings KPASSes

[gdb/testsuite] Fix minimal encodings KPASSes

With current master I see a couple of KPASSes:
...
KPASS: gdb.ada/enum_idx_packed.exp: scenario=minimal: ptype small \
  (PRMS minimal encodings)
  ...
KPASS: gdb.ada/mod_from_name.exp: scenario=minimal: print xp \
  (PRMS minimal encodings)
KPASS: gdb.ada/pckd_arr_ren.exp: scenario=minimal: print var \
  (PRMS minimal encodings)
...

The corresponding setup_kfail is called for everything before gnat 11.

However, the test-cases also PASS for me with gnat-4.8, gnat-7.5.0 and
gnat-8.4.0.

Fix the KPASSes by limiting the setup_kfail to gnat 9 and 10.

Tested on x86_64-linux.

gdb/testsuite/ChangeLog:

2020-11-23  Tom de Vries  <tdevries@suse.de>

	* gdb.ada/enum_idx_packed.exp: Limit setup_kfail to gnat 9 and 10.
	* gdb.ada/mod_from_name.exp: Same.
	* gdb.ada/pckd_arr_ren.exp: Same.